1. Field of the Invention
The present invention relates generally to the field of digital measurement systems, and more specifically to a calibration utility used to calibrate analog signals obtained from a sensor in a non-linear measurement system.
2. Description of the Related Art
Today's safety critical systems, such as medical products or surgical equipment, require highly accurate measurement of vacuum and pressure to ensure proper instrument control and safe use in an operating theater. In a medical environment, a precision surgical device, such as a phacoemulsification machine, typically includes a pressure sensor that converts detected pressure into a representative or proportional physical motion to control said pressure. The machine measures the resultant analog or continuous signal produced due to this physical motion and converts the signal produced into a digital representation. This digital representation or signal can be transmitted to the machine's system processor and used to display the measured pressure values in human readable units (e.g. mmHg).
Current safety critical system designs can hinder system performance and ultimately cause harm to the patient in that the relationship between the detected physical pressures or sensor component motions read or encountered by the sensor and the corresponding actual values may differ by an unquantifiable amount, or their relationship may be non-linear. For example, the measurement system may measure an analog signal of 1000 units of motion from the pressure sensor that represents an actual pressure of 100 mmHg. The system may measure an analog signal of 500 units of pressure or motion from the same pressure sensor that represents an actual pressure of approximately 30 mmHg, more or less, making correlating movement to pressure difficult and inexact. Further, the system may exhibit non-linear effects where the extent of the resultant non-linear output may vary over different segments of the measurement range of the pressure sensor. In this situation, the system may generate analog signals that are, for example, very close to being linear at one end of the measurement range and less linear at the other end of the systems measurement range. The amount or actual extent of the systems non-linearity found in current designs depends upon numerous factors including the sensor mechanism used to convert pressure, or another parameter such as altitude, speed, time, or volume, to motion, the motion measurement system employed, and the method used to convert the analog measurement into a digital representation or signal.
A major commercial problem with regard to current designs is that such designs rely on a manual procedure to calibrate the system. For example, to calibrate a typical phacoemulsification system, an operator connects a syringe or other manual pressure-generating device to provide a baseline pressure input. The operator generates a known amount of pressure and measures the output using the measurement system. Typically, two points are measured; one at the low end and the other at the high end of the system's measuring range. The operator assumes the measurement system to be linear across the range of values between these two measured points. The operator then uses interpolation to derive addition values for any arbitrary measured value between these two measured points in order to determine the actual pressure. Such manual calibration techniques have many issues, not the least of which is the operator being required to generate a precise amount of pressure at two points along the system's measurement range. Generating a precise amount of pressure using a manual device is awkward for the operator and difficult to perform consistently and reliably, particularly at the extreme ends of the systems measurement range. Moreover, many of today's measurement systems are non-linear over a portion or the entire range of the measurement system and will not produce accurate measurements when calibrated using manual calibration techniques.
Thus, today's measurement system designers are faced with a difficult and complex implementation challenge to ensure accurate, consistent, and precise calibration of non-linear measurement systems to provide proper control and feedback of the surgical instrument, found in the phacoemulsification machine example, and the required level of safety in an operating theater or other safety critical environment.
Based on the foregoing, it would be advantageous to provide a measurement calibration utility for use in safety critical systems that overcomes the foregoing drawbacks present in previously known manual procedures used in the operation and calibration of measurement systems.